The present invention relates to sensors and related methods and computer program products, and more particularly, to vibrating-conduit measurement apparatus, methods and computer program products.
Vibrating conduit sensors, such as Coriolis mass flowmeters, typically operate by detecting motion of a vibrating conduit that contains a material. Properties associated with the material in the conduit, such as mass flow, density and the like, in the conduit may be determined by processing signals from motion transducers associated with the conduit, as the vibrational modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flowmeter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries and the like, in the system. Each conduit may be viewed as having a set of natural vibrational modes including, for example, simple bending, torsional, radial and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited at resonance in one of its natural vibrational modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time or phase differences between motion at the transducer locations. Exemplary Coriolis mass flowmeters are described in U.S. Pat. No. 4,109,524 to Smith, U.S. Pat. No. 4,491,025 to Smith et al., and U.S. Pat. No. Re. 31,450 to Smith.
The accuracy of Coriolis mass flowmeters may be compromised by nonlinearities and asymmetries in the conduit structure, motion arising from extraneous forces, such as forces generated by pumps and compressors that are attached to the flowmeter, and motion arising from pressure forces exerted by the material flowing through the flowmeter conduit. For example, variations in forces applied to an unbalanced Coriolis mass flowmeter arising from variations in mounting conditions may significantly affect its performance. The effects of these forces may be reduced by using flowmeter designs that are balanced to reduce effects attributable to external vibration, and by using signal processing techniques to compensate for unwanted components of motion. However, variations in environmental conditions and mounting conditions may still introduce bias or other inaccuracies into measurements made according to such techniques.
According to embodiments of the present invention, a parameter sensor including a conduit configured to contain a material is controlled. A first excitation applied to the conduit is determined. Motion of the conduit in response to the first excitation is determined. A second excitation to apply to the conduit is determined from the determined first excitation, the determined motion in response to the first excitation, and a desired motion for the conduit. The second excitation is then applied to the conduit.
In particular, according to some embodiments of the present invention, the desired motion includes a desired periodic motion at the predetermined frequency. Determining the first excitation includes determining a first periodic excitation at the predetermined frequency. Determining motion of the conduit in response to the first excitation includes determining periodic motion at the predetermined frequency in response to the first periodic excitation. Determining a second excitation includes determining a second periodic excitation at the predetermined frequency to apply to the conduit from the determined first periodic excitation, the determined periodic motion at the predetermined frequency in response to the first periodic excitation, and the desired periodic motion. Applying the second excitation includes applying the second periodic excitation to the conduit.
According to some embodiments of the present invention, a second excitation to apply to the conduit is determined from a determined previous first excitation, a determined motion in response to the first excitation, a desired motion for the conduit, and a frequency response for the conduit. In some embodiments of the present invention, the frequency response is assumed to be time-invariant. In other embodiments of the present invention, the frequency response is adaptively determined. For example, the frequency response may be determined according to a recursive least squares estimation procedure, such as a weighted recursive least squares estimation procedure.
For example, in some embodiments, adaptively determining the frequency response includes generating a first estimated frequency response and then generating a second estimated frequency response from the first estimated frequency response, the determined first excitation, and the determined motion of the conduit in response to the first excitation. Determining a second excitation includes determining the second excitation from the determined first excitation, the desired motion, the determined motion in response to the first excitation, and at least one of the first estimated frequency response and the second estimated frequency response. In particular, the first estimated frequency response may include a first estimated inverse frequency response, the second estimated frequency response may include a second inverse estimated frequency response, and the second excitation may be determined from the determined first excitation, the desired motion, the determined motion in response to the first excitation, and at least one of the first estimated inverse frequency response and the second estimated inverse frequency response.
According to some embodiments, a plurality of drive signals is generated based on the determined first excitation, the determined motion in response to the first excitation, a desired motion for the conduit, and the frequency response. The plurality of drive signals is applied to a plurality of actuators operatively associated with the conduit to generate the second excitation. The desired motion may include a desired periodic motion at the predetermined frequency and the desired motion may be represented by a phasor representation of the desired periodic motion at the predetermined frequency. Determining a first excitation may include generating a phasor representation of a first periodic excitation at the predetermined frequency. Determining motion of the conduit in response to the first excitation may include processing motion signals representing the motion of the conduit in response to the first excitation to generate a phasor representation of motion of the conduit at the predetermined frequency in response to the first excitation. Generating a plurality of drive signals may include generating a phasor representation of a second periodic excitation at the predetermined frequency from the phasor representation of the first periodic excitation, the phasor representation of the desired motion, the phasor representation of motion of the conduit at the predetermined frequency in response to the first excitation, and the frequency response, and generating the plurality of drive signals from the phasor representation of the second periodic excitation.
According to other embodiments of the present invention, a process parameter associated with a material contained in a conduit is determined. The conduit is excited by iteratively determining and applying new excitations to the conduit and determining motion in response to the applied new excitations such that a new excitation is determined based on a previously determined excitation, a determined motion in response to the previously determined excitation, a desired motion for the conduit, and a frequency response for the conduit. Motion signals representative of motion of the excited conduit are processed to generate an estimate of a process parameter, e.g., a mass flow parameter such as mass flow rate, associated with a material contained in the conduit.
The conduit may be excited such that motion at a location of the conduit is constrained to approximate a predetermined motion. For example, the conduit may be excited such that motion of the conduit is constrained to approximate a predetermined boundary condition for a real normal mode of the conduit. The motion signals may be processed according to a procedure that assumes the predetermined boundary condition to generate the parameter estimate.
In still other embodiments of the present invention, an apparatus is provided for controlling a parameter sensor including a conduit configured to contain a material, a plurality of actuators operative to move the conduit responsive to drive signals, and a plurality of motion transducers operative to generate motion signals representative of motion of the conduit. The apparatus includes a shape control circuit configured to be coupled to the motion transducers and to the actuators. The shape control circuit is operative to apply a first plurality of drive signals to the plurality of actuators to apply a first excitation to the conduit, to process motion signals received from the plurality of motion transducers to determine motion of the conduit in response to the first excitation, and to apply a second plurality of drive signals to the plurality of actuators based on the first excitation, the determined motion in response to the first excitation, and a desired motion for the conduit to thereby apply a second excitation to the conduit. The shape control circuit may further include a frequency response determiner circuit operative to adaptively determine a frequency response of the conduit, and may generate the second plurality of drive signals based on the first excitation, the determined motion in response to the first excitation, the desired motion for the conduit, and the determined frequency response.
In other embodiments of the present invention, a process parameter sensor includes a conduit configured to contain a material, a plurality of actuators operatively associated with the conduit, and a plurality of motion transducers operatively associated with the conduit. The sensor further includes a shape control circuit configured to receive motion signals-from the plurality of motion transducers and to apply drive signals to the plurality of actuators. The shape control circuit is operative to excite the conduit by iteratively determining and applying new excitations to the conduit and determining motion in response to the applied new excitations such that a new excitation is determined based on a previously determined excitation, a determined motion in response to the previously determined excitation, and a desired motion for the conduit. A process parameter estimator circuit is configured to receive motion signals from the plurality of motion transducers and operative to process the received motion signals to generate an estimate of a process parameter, e.g., mass flow rate, associated with a material contained in the conduit.
According to other embodiments of the present invention, a computer program product is provided for controlling a parameter sensor including a conduit configured to contain a material, a plurality of actuators operatively associated with the conduit, and a plurality of motion transducers operatively associated with the conduit. The computer program product includes computer-readable program code embodied in a computer readable storage medium. The computer-readable program code includes program code, responsive to the motion transducers, for determining motion of the conduit in response to a known first excitation applied to the conduit. The computer-readable program code further includes program code, responsive to the program code for determining motion, for determining a second excitation to apply to the conduit from the known first excitation, the determined motion in response to the first excitation, and a desired motion for the conduit. The computer-readable program code further includes program code for causing the plurality of actuators to apply the second excitation to the conduit.